Fibroblast growth factors (FGF) are angiogenic polypeptide mitogens with mitogenic activity for a wide variety of cell types, see reviews: Gospodarowicz et al., Endocrine Reviews 8:95-113 (1987); Burgess and Maciag, Annu. Rev. Biochem. 58:575-606 (1989); Gospodarowicz, Clin. Orthop. Relat. R. 257:231-248 (1990); Baird and Bohlen, In Peptide Growth Factors and Their Receptors 1, pp. 369-418, Springer-Verlag, Berlin (1990). Fibroblast growth factors are classified either as acidic fibroblast growth factor (aFGF) with a molecular mass of about 15.9 kDa or basic fibroblast growth factor (bFGF) with a molecular mass of about 16.3 kDa. A distinctive feature of FGF is a dependence on the presence of polyanions such as heparin for in vitro biological activity and structural integrity: Gospodarowicz et al., Endocrine Reviews 8: 95-113 (1987); Burgess and Maciag, Annu. Rev. Biochem. 58: 575-606 (1989); Gospodarowicz, Clin. Orthop. Relat. R. 257: 231-248 (1990); Baird and Bohlen, In Peptide Growth Factors and Their Receptors 1, pp. 369-418, Springer-Verlag, Berlin (1990). Like a wide variety of plasma proteins, FGF interacts strongly with heparin and is often isolated by affinity chromatography using heparin as a ligand with different salt concentration required for elution: aFGF, 1.0 M; bFGF, 1.6 M. One striking manifestation of the FGF/heparin interaction is protection of the growth factor from proteolytic, acidic and thermal inactivation: Gospodarowicz and Cheng, J. Cell Physiol. 128: 475-484 (1986); Rosenbart et al., Biochem. Biophys. Res. Comm. 152:432-440 (1988); Sakesla et it1., J. Cell Biol. 107: 743-751 (1988), Mueller et al., J. Cell Physiol. 140:439-448 (1989); Sommer and Rifkin J. Cell Physiol. 138:215-220 (1989). In vivo, the protein is often found associated extracellularly with heparan sulfate proteoglycans which presumably provide a natural stabilizing environment: Klagsbum, Cur. Opin. Cell Biol. 2:857-863 (1990); Sakaguchi et al., J. Biol. Chem. 266:7270-7278 (1991); Yayon et al., Cell 64: 841-848 (1991). It has been postulated that release of FGF from the extracellular matrix by heparanases is used to regulate the availability of active growth factor, Vlodavsky, et al., J. Cell. Biochem. 45:167-176 (1991). This may also explain the lack of a conventional signal sequence in the protein, Gospodarowicz et al., Endocrine Reviews 8:95-113 (1987); Burgess and Maciag, Annu. Rev. Biochem. 58:575-606 (1989); Gospodarowicz, Clin. Orthop. Relat. R. 257:231-248 (1990); Baird and Bohlen, In Peptide Growth Factors and Their Receptors 1, pp. 369-418, Springer-Verlag, Berlin (1990).